Electrical contact



Jan. 14, 1930. T. s. FULLER 1,743,763

ELECTRICAL CONTACT Filed Sept. 16, 1926 Copper SiIiCO'n AI log Inventor: Truman S. Ful Ier,

bg His Attorney.

Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE ASSIGNOR TO GENEBALELECTRIC NEW YORK uncommon. conmcr Application filed September 16, 1926. Serial No. 135,836.

This invention relates to electrical contacts, particularly contacts for electric switches.

The object of the invention is to provide an improved circuit making and breaking contact that has a substantial current-carrying capacity, as well as a relatively low and uniform contact resistance throughout a long period of circuitinterrupting service.

The contact resistance encountered in the ordinary form of circuit-controlling switch is an inherent characteristic that determines to a large degree the safe continuous currentcarrying capacity of the switch. This is particularly true in switches designed for controlling heavy current circuits where the contact resistance and the resulting heating of the switch contacts readily may become the predominating factor controlling the maximum rating of the switch. In such switches copper is the material principally used for all current-carrying parts, as it has the lowest ohmic resistance, as well as the highestheat conductivity of any of the cheaper metals. However, switch contacts formed of copper soon become oxidized in service. Since the copper oxide is a very poor conductor of current, the contact resistance of the switch may be increased many times its initial value. The resulting heating of the switch contacts with normal current flow may become so excessive as to render the switch unsafe for continued service.

The difficulties due to contact resistance are overcome in accordance with my present invention b forming the contacts of copper alloyed with silicon. I have found that a small percentage of silicon alloyed with the copper, as for example 1 or 2% of silicon, results in a material that has an initial contact resistance, not materially greater than copper alone, and which will maintain the contact resistance at a fairly uniform value over a long period of circuit making and breaking service. As the contact is formed of a homogeneous composition, the contact resistance characteristics are retained even though the initial contact surface is burned away or pitted by the arcing to which the switch contact is subjected.

As illustrating a preferred way in which the invention may be carried into effect, I have shown in the accompanying drawing a switch contact of the usual type employed in heavy duty switches or contactors which is formed of an alloy comprising copper and silicon in accordance with my invention.

he particular manner in which copper- SlllCOIl alloy is produced-is not material to the present invention so long as a fairly homogeneous product is obtained, and any ordinary process of alloying the silicon with the copper may be used. However, I have found that the silicon content of the alloy need not exceed substantially 2%, as contacts formed of alloys having a greater silicon content are no better in service than with a lesser silicon content. The best results may be obtained with a switch contact formed of an allow comprlsmg substantially 99% of copper and 1% of silicon. With contacts formed of an alloy of this constituency the contact resistance remains substantially uniform at a relatively low .value during long continued service in heavy current switches. Furthermore, the inevitable roughening of the surface of the switch contacts due to pitting and burning by the are necessarily occurring upon establishing and interrupting the circuit do not materially vary the contact resistance of the contacts. This probably is due to the fact that under any conditions the actual contact is made only at relatively few points.

Due to the substantially uniform low contact resistance of my improved contacts, there is no substantial heating localized at the contact surfaces even after the contact has been in service for a long period. This permits the current-carrying rating of an ordinary type of switch equipped with my improved contacts to be materially increased without exceeding permissible temperatures and in this way effects a material saving in providing switches of the increased rating.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A circuit-interrupting switch contact formed of a metal alloy consisting of copper and silicon.

2. A. circuit-interrupting switch contact composed rincipally of copfier and a relatively sma percentage ofsi "con.

3. A circuit-interrupting switch contact formed of copper alloyed with less than 2% of silicon. v

4. A circuit-interrupt' g switch contact composed of a. co per silicon alloy of 99% copper and 1% silicon.

In witness whereof, I have hereunto set my hand this 14th day of September 1926.

TRUMAN S. FULLER. 

